The invention relates to a process for the feeding of fluid additives to the fluid contained in a fluid system and, in particular, the feeding of replenishers to a photographic processing fluid contained in a photographic processing tank, wherein the fluid additive is entered at the first end of a feeding duct connected with the fluid system and discharged into the fluid system from a second end of said feeding duct.
Moreover, the invention relates to a device for feeding such a fluid additive. The device comprising a feeding duct whose first end is connected with the supply vessel for the fluid additive to be supplied and whose second end is connected with the fluid system to be supplied, further comprising at least one fluid feed pump and a valve arrangement which can be actuated by a control circuit and in which the feeding duct can be selectively cleared and blocked.
Feeding processes and devices of this type are known already. See, for example, EP 0 216 791 Bl. A preferred field of application of such processes and devices is the supply of a photographic processing fluid to photographic processing tanks. For this purpose a metered supply of fluid additives is provided such that the substances of the processing fluid consumed during operation are replenished in a suitable manner so that the processing fluid contained in the tank is regenerated, i.e., maintains or regains its functional properties. If the tank to be supplied is a developer tank it may be water, for example, and a number of concentrates each containing a component of the developer solution that have to be metered to the tank. If it is a fixing bath it is also water and at least one concentrate in the form of a concentrated fixing salt solution which are to be supplied for replenishment.
It is the object of the invention to provide a process which ensures a particularly reliable and economic supply of fluid additives to a system fluid and which is suitable in particular for the feeding of replenishers into photographic processing tanks.
In a process of the above type, this object is attained in accordance with the invention in that when different fluid additives are to be supplied, such fluids are successively fed into the feeding duct and in that prior to the feeding in of a fluid additive which differs from the fluid additive successively to be fed in, at least the area of the first end of the feeding duct is filled with system fluid.
Since the entrance area of the feeding duct is filled with system fluid before the fluid additive is fed, one single feeding duct can be used for all fluid additives, no matter what their chemical and physical properties are like. This was not possible so far because when certain concentrates are brought into direct contact or mixed, undesired chemical reactions occur which may lead, for example, to the formation of gases or the precipitation of substances. In the process according to the invention this danger is excluded because all additives are metered into the system fluid by which the feeding duct has previously been filled.
The invention not only offers an opportunity of using only one single feeding duct independently of the chemical nature of the fluid additives to be fed in, but also a further particularly advantageous opportunity of measuring the volume of the fluid additives supplied by means of a single flow meter which is arranged within the feeding duct.
If the fluid additives are also physically different a single flow meter may also be used subject to its arrangement in a location through which only system fluid flows during metering. In this manner a single flow meter exclusively calibrated for the system fluid can serve for determining the volume irrespectively of the fluid additive supplied. Owing to the great differences in the physical properties (viscosity and the like) of the various additives a flow meter specially calibrated for each of such fluid additives would otherwise be necessary.
In the case of a preferred embodiment, the feeding duct is filled with the system fluid using a fluid circulation system in which the system fluid is fed out of the fluid system by means of a feed pump and conveyed via a feedback duct to the first end of the feeding duct, such circulation being interrupted by the blocking of said feedback valve prior to the supply of another fluid additive into the feeding duct of the fluid circulation system and only cleared again when subsequent to such feeding, the feeding duct is once again to be filled with system fluid. In the case of such an embodiment the feeding duct can be constantly flushed with system fluid between successive supply operations so that it can be ensured that when another supply operation is initiated, the feeding duct is filled with fresh system fluid.
It is also an object of the invention to provide a device which is particularly suitable for the supplying of fluid additives to the system fluid :n a fluid system, and in particular of replenishers for a photographic processing fluid contained in a photographic processing tank.